INFO: rcu detected stall in neigh_timer_handler (3)

Status: upstream: reported on 2026/08/07 01:39
Reported-by: syzbot+77594b6302d7010c94e4@syzkaller.appspotmail.com
First crash: 23d, last: 7d12h
▶ ▼ Similar bugs (27)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in neigh_timer_handler (6) netfilter 1 1 2090d 2090d 0/29 auto-closed as invalid on 2021/03/09 03:20
linux-6.6 INFO: rcu detected stall in neigh_timer_handler 1 1 179d 179d 0/2 auto-obsoleted due to no activity on 2026/06/12 03:02
upstream INFO: rcu detected stall in neigh_timer_handler (8) net 1 syz, C done done 72 748d 808d 28/29 fixed on 2024/10/21 12:45
upstream INFO: rcu detected stall in neigh_timer_handler net 1 1 2835d 2835d 0/29 auto-closed as invalid on 2019/05/23 06:47
upstream INFO: rcu detected stall in neigh_timer_handler (2) net 1 2 2545d 2546d 13/29 fixed on 2019/10/09 10:54
upstream INFO: rcu detected stall in neigh_timer_handler (4) net 1 1 2460d 2460d 0/29 closed as invalid on 2019/12/04 14:04
linux-5.15 INFO: rcu detected stall in neigh_timer_handler 1 1 349d 349d 0/3 auto-obsoleted due to no activity on 2025/12/23 11:36
upstream INFO: rcu detected stall in neigh_timer_handler (5) net 1 1 2192d 2192d 0/29 auto-closed as invalid on 2020/11/26 10:25
linux-6.6 INFO: rcu detected stall in neigh_timer_handler (2) 1 1 35d 35d 0/2 upstream: reported on 2026/07/25 18:11
linux-5.15 INFO: rcu detected stall in neigh_timer_handler (2) 1 2 186d 188d 0/3 auto-obsoleted due to no activity on 2026/06/04 18:05
upstream INFO: rcu detected stall in neigh_timer_handler (3) net 1 2 2465d 2465d 0/29 closed as invalid on 2019/11/29 14:24
linux-6.1 INFO: rcu detected stall in neigh_timer_handler (3) 1 1 318d 318d 0/3 auto-obsoleted due to no activity on 2026/01/23 04:30
upstream INFO: rcu detected stall in neigh_timer_handler (7) net 1 1 1965d 1965d 0/29 auto-closed as invalid on 2021/07/11 19:14
linux-6.1 INFO: rcu detected stall in neigh_timer_handler (2) 1 1 572d 572d 0/3 auto-obsoleted due to no activity on 2025/05/14 07:23
linux-4.14 INFO: rcu detected stall in neigh_timer_handler 1 5 2310d 2429d 0/1 auto-closed as invalid on 2020/08/30 16:21
linux-6.1 INFO: rcu detected stall in neigh_timer_handler 1 4 703d 814d 0/3 auto-obsoleted due to no activity on 2025/01/03 05:12
upstream BUG: soft lockup in neigh_timer_handler (2) net 1 2 583d 613d 0/29 closed as invalid on 2025/02/28 15:46
upstream BUG: soft lockup in neigh_timer_handler (4) perf 1 1 154d 154d 0/29 closed as invalid on 2026/05/19 12:17
android-5-10 BUG: soft lockup in neigh_timer_handler 1 2 1101d 1110d 0/2 auto-obsoleted due to no activity on 2023/11/22 05:43
linux-4.19 BUG: soft lockup in neigh_timer_handler 1 4 1386d 1645d 0/1 auto-obsoleted due to no activity on 2023/03/12 06:57
android-54 BUG: soft lockup in neigh_timer_handler (2) 1 5 471d 556d 0/2 auto-obsoleted due to no activity on 2025/08/13 05:16
linux-4.14 BUG: soft lockup in neigh_timer_handler 1 3 1655d 1698d 0/1 auto-closed as invalid on 2022/06/16 21:59
android-5-15 BUG: soft lockup in neigh_timer_handler 1 1 50d 50d 0/2 premoderation: reported on 2026/07/10 13:24
upstream BUG: soft lockup in neigh_timer_handler (3) batman 1 2 483d 484d 0/29 auto-obsoleted due to no activity on 2025/08/01 18:42
android-6-1 BUG: soft lockup in neigh_timer_handler 1 2 1016d 1038d 0/2 auto-obsoleted due to no activity on 2024/02/16 02:11
android-54 BUG: soft lockup in neigh_timer_handler 1 3 800d 812d 0/2 auto-obsoleted due to no activity on 2024/09/18 13:19
upstream BUG: soft lockup in neigh_timer_handler net 1 1 1134d 1108d 0/29 auto-obsoleted due to no activity on 2023/10/20 21:15

Sample crash report:
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-....: (1 GPs behind) idle=227/1/0x4000000000000000 softirq=54347/54348 fqs=3100 
	(t=10501 jiffies g=75305 q=8587)
rcu: rcu_preempt kthread timer wakeup didn't happen for 4278 jiffies! g75305 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=1 timer-softirq=56293
rcu: rcu_preempt kthread starved for 4281 jiffies! g75305 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:I stack:27216 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
 rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 7409 Comm: kworker/u4:15 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: wg-kex-wg1 wg_packet_handshake_send_worker
RIP: 0010:queued_write_lock_slowpath+0x129/0x270 kernel/locking/qrwlock.c:78
Code: f0 41 81 0e 00 01 00 00 43 0f b6 04 27 84 c0 74 37 44 89 f1 80 e1 07 80 c1 03 38 c1 7c 2a 4c 89 f7 e8 0b e2 5f 00 eb 20 f3 90 <43> 0f b6 04 27 84 c0 74 15 44 89 f1 80 e1 07 80 c1 03 38 c1 7c 08
RSP: 0018:ffffc90002eff440 EFLAGS: 00000206
RAX: 00000000000001ff RBX: ffffc90002eff490 RCX: ffffffff815e3f8f
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffff88807814d828
RBP: ffffc90002eff4f0 R08: ffff88807814d82b R09: 1ffff1100f029b05
R10: dffffc0000000000 R11: ffffed100f029b06 R12: dffffc0000000000
R13: 1ffff920005dfe8c R14: ffff88807814d828 R15: 1ffff1100f029b05
FS:  0000000000000000(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000556330c68a38 CR3: 0000000072794000 CR4: 00000000003506e0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <TASK>
 queued_write_lock include/asm-generic/qrwlock.h:97 [inline]
 do_raw_write_lock+0x1e6/0x260 kernel/locking/spinlock_debug.c:210
 __neigh_event_send+0x32/0x1410 net/core/neighbour.c:1118
 neigh_event_send include/net/neighbour.h:438 [inline]
 neigh_resolve_output+0x1ab/0x6a0 net/core/neighbour.c:1488
 neigh_output include/net/neighbour.h:509 [inline]
 ip6_finish_output2+0x108b/0x1530 net/ipv6/ip6_output.c:130
 ip6tunnel_xmit include/net/ip6_tunnel.h:160 [inline]
 udp_tunnel6_xmit_skb+0x4b7/0x8b0 net/ipv6/ip6_udp_tunnel.c:110
 send6+0x5a0/0x8d0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0x10d/0x1c0 drivers/net/wireguard/socket.c:178
 wg_packet_send_handshake_initiation drivers/net/wireguard/send.c:40 [inline]
 wg_packet_handshake_send_worker+0x203/0x360 drivers/net/wireguard/send.c:51
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
NMI backtrace for cpu 0
CPU: 0 PID: 18454 Comm: syz.0.2785 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_dump_cpu_stacks+0x22d/0x380 kernel/rcu/tree_stall.h:349
 print_cpu_stall+0x31f/0x5f0 kernel/rcu/tree_stall.h:633
 check_cpu_stall kernel/rcu/tree_stall.h:727 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x6ec/0x1120 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:2021
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4b0/0xb60 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x397/0x8b0 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x4d/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:kasan_quarantine_put+0x84/0x210 mm/kasan/quarantine.c:234
Code: e8 51 fa c0 ff 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 0f 85 83 00 00 00 41 f7 c7 00 02 00 00 74 01 fb 31 c0 <48> 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f c3 48 8d 80 40 62 03 00 45
RSP: 0018:ffffc90000007920 EFLAGS: 00000206
RAX: ac694a0030d95301 RBX: ffff88802631a000 RCX: ac694a0030d95300
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a4280
RBP: ffffc900000079b0 R08: ffffffff901ef197 R09: 1ffffffff203de32
R10: dffffc0000000000 R11: fffffbfff203de33 R12: ffff888016c42000
R13: ffff88802631a000 R14: 0000000000081840 R15: 0000000000000286
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 skb_free_head net/core/skbuff.c:655 [inline]
 skb_release_data+0x667/0x830 net/core/skbuff.c:677
 skb_release_all net/core/skbuff.c:742 [inline]
 __kfree_skb net/core/skbuff.c:756 [inline]
 kfree_skb_reason+0xaf/0x110 net/core/skbuff.c:776
 kfree_skb include/linux/skbuff.h:1118 [inline]
 __skb_queue_purge include/linux/skbuff.h:2978 [inline]
 neigh_invalidate+0x39b/0x460 net/core/neighbour.c:1004
 neigh_timer_handler+0x90d/0xff0 net/core/neighbour.c:1088
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x56c/0x810 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:finish_lock_switch+0x12f/0x290 kernel/sched/core.c:4804
Code: 83 c7 18 be ff ff ff ff e8 6e 4b 6c 08 85 c0 74 46 4d 85 ff 75 62 0f 1f 44 00 00 48 89 df e8 98 ba 75 08 e8 23 d8 2a 00 fb 5b <41> 5c 41 5d 41 5e 41 5f 5d c3 48 89 df e8 2f 0e fe ff 43 80 3c 2c
RSP: 0018:ffffc9000332f7d8 EFLAGS: 00000286
RAX: ac694a0030d95300 RBX: ffff88813fe29dc0 RCX: ac694a0030d95300
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a4280
RBP: 1ffff11017207613 R08: ffffffff901ef1cf R09: 1ffffffff203de39
R10: dffffc0000000000 R11: fffffbfff203de3a R12: 1ffff110172075c1
R13: dffffc0000000000 R14: ffff8880b903ae08 R15: 0000000000000000
 finish_task_switch+0x12f/0x650 kernel/sched/core.c:4921
 context_switch kernel/sched/core.c:5052 [inline]
 __schedule+0x11cb/0x4350 kernel/sched/core.c:6395
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 smp_call_function_single+0x42b/0x4c0 kernel/smp.c:760
 task_function_call kernel/events/core.c:120 [inline]
 perf_install_in_context+0x5cf/0x930 kernel/events/core.c:3016
 __do_sys_perf_event_open kernel/events/core.c:12793 [inline]
 __se_sys_perf_event_open+0x12b3/0x1bb0 kernel/events/core.c:12387
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f141425c0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f14124b4028 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: ffffffffffffffda RBX: 00007f14144e3fa0 RCX: 00007f141425c0d9
RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 0000200000000480
RBP: 00007f14142f3024 R08: 000000000000000a R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007f14144e4038 R14: 00007f14144e3fa0 R15: 00007fffc5c2e838
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/22 15:45 linux-5.15.y 0eb903b5b519 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in neigh_timer_handler
2026/08/07 01:38 linux-5.15.y 9c7634c60784 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in neigh_timer_handler
* Struck through repros no longer work on HEAD.